There is known a technique of attaching an RFID (Radio Frequency IDentification) tag to a sample container such as a test tube containing a sample, and using an antenna which reads the RFID tag to read information stored in the RFID tag or store information in the RFID tag.
It is known that a radio wave may be absorbed by the sample or surrounding substance, depending on a radio wave frequency, which may lead to decreased accuracy of reading or writing information from or to the RFID tag.
International Publication Pamphlet No. WO2006/077645
Since the electric field of a patch antenna generally used for reading an RFID tag is not uniform, there has been a problem that reading or writing information simultaneously from or to each of RFID tags attached to a plurality of sample containers may cause read or write errors in some of the sample containers. Therefore, the number of readings or writings has been limited to about 50 when reading from or writing to a plurality of tags. In addition, a non-uniform electric field prevents stable reading or writing, and therefore the sample containers needed to be moved in the course of reading or writing in order to pass an electric field that allows reading or writing through the sample containers.